Vibration generally, and particularly of structural elements supporting humans and sensitive equipment and apparatus, can have many negative effects. Such negative effects can include, but are not limited to, discomfort to, and premature fatigue of, human operators and passengers, and noise and degradation of equipment.
A category or type of vibrations generated during operation of vehicles, and particularly, work machines such as those used in agricultural, construction, mining, forestry and earthmoving applications, hereinafter sometimes collectively referred to by the term “work machine”, is low frequency, relatively high amplitude vibrations, having generally horizontal or planar vectors or components. Such low frequency horizontal vibrations can be especially discomforting to human operators and passengers of the vehicles and machines who are supported on structures such as operator and passenger cabs and seats, and who are subjected to such vibrations for long periods of time.
Vibrations of this category can include horizontal vibrations, including fore and aft and side-to-side vibrations; pitch vibrations; roll vibrations; and yaw vibrations, and can result from one or more sources, including environmental and external sources, such as rough terrain and roads over which a work machine passes, and internal sources, such as engine and power train operation, lugged wheel rotation, and particularly, operation of various systems of a work machine. In this latter regard, agricultural work machines, and specifically harvesting machines such as combines, windrowers and cotton harvesters, can include multiple operating systems in addition to the power plant and drive train, which generate a multitude of potentially annoying and discomforting low frequency vibrations. Towing loads, such as grain carts, by a harvesting machine or tractor, can also generate these types of vibratory movements. Such vibrations and vibratory movements are typically within a range of from about 1 to about 20 cycles per second (Hz), and up to as much as about 100 Hz, and can have a wide variety of amplitudes, for instance, of as much as 15 millimeters. The characteristics of the rubber mount will not effectively isolate the low frequency vibrations in the horizontal or vertical directions. Accordingly, generally horizontal, low frequency, high amplitude vibrations and resulting vibratory movements of structural elements of work machines such as those set forth above have been found to be particularly problematic and difficult to isolate or reduce.
Compounding this difficulty, is that a work machine such as a combine, windrower or cotton harvester, may have several sources generating these vibrations in different directions. Examples of systems on a typical agricultural combine which have been found to generate particularly annoying and discomforting low frequency vibrations include the sidewardly reciprocating cutter knife or sickle bar of a small grain header; the fore and aft reciprocating cleaning shoes or sieves of the cleaning system; and various rotating apparatus, including the rotary separator, and numerous conveyor devices. Large lugged tires can also generate annoying low frequency, low amplitude vibrations when rolling.
A variety of mounts and support structures for operator and passenger cabs and platforms, seats, and the like, have been proposed for isolating, damping, and attenuating vibrations of work machines and vehicles. Reference in this regard Ochsner U.S. Pat. No. 4,271,921, issued Jun. 9, 1981 to Deere & Company; Hoefle U.S. Pat. No. 5,368,118, issued Nov. 29, 1994 to Deere & Company; and Higuchi U.S. Pat. No. 6,340,201, issued Jan. 22, 2002 to Hitachi Construction Machinery Co., Limited. However, observed shortcomings of these and other known proposed devices variously include, high complexity and expense; requirements of tuning for achieving desired vibration attenuation; and, in the instance of the latter referenced patent, possible increases in horizontal vibratory movements as a consequence of reducing occurrences of pitching, rolling and yawing vibrations.
It is also well known to use rubbery, viscous, and pneumatic devices for vibration isolation. Essentially, known devices of these types simulate a spring and damper system in connection with a movable mass, for reducing vibration transmission. However, it has been found that such devices still provide only poor reduction of transmission or isolation of the low frequency horizontal vibration and vibratory movements identified as problems above. In particular, known rubbery vibration isolators have been found to only provide satisfactory vibration isolation when the forcing frequency fd of the vibration is significantly larger than the natural frequency fn of the isolator itself. And, when the forcing frequency fd is near or less than the natural frequency fn, the isolator can actually amplify the vibration. One proposed approach to isolate low frequency vibration has been to use a pneumatic mount that has a very low natural frequency. However, this has been found to have negative effects, including high costs, and large size. The effectiveness of pneumatic devices can also be temperature sensitive.
Thus, what is sought is a vibration isolator adapted for isolating low frequency vibrations and vibratory movements, particularly high amplitude, horizontal components or vectors thereof, which overcomes one or more of the shortcomings and/or limitations set forth above, and which is adapted for use in connection with support structures and elements for holding or carrying human operators and passengers on vehicles and work machines, such as agricultural harvesting machines, tractors and the like.